Graffiti on windows in public areas has been a longstanding problem, particularly for windows on public transportation systems, such as subways and buses. One solution to the problem of graffiti on windows has been the mounting of transparent shields or guard panels on the windows. As a result, graffiti collects on the shield rather than the window. These graffiti shields are typically plastic and disposable. The windows themselves are often much more expensive to replace than a disposable plastic graffiti shield. When an undesirable amount of graffiti is present on the shield, the shield can be removed, disposed of, and replaced without replacing the window.
There have been various approaches to mounting the graffiti shields over the windows. One solution has been to use retaining strips which hold the graffiti shield over the window by clamping the edge of the shield between the strips and the window or the frame. The retaining strips are held to the frame with screws. By tightening the screws, the strips hold the graffiti shield in place. Another solution has been to use double-sided tape. The tape is applied directly to the face of the graffiti shield and then the shield is attached to the window or to the frame.
Both of these solutions to the problem of mounting the graffiti shield over the window have significant disadvantages. Using retaining strips held in place by screws is inefficient because the initial installation of the strips is difficult and expensive. In addition, replacing the graffiti shield is time consuming, as all of the strips must be removed by unscrewing the screws one by one. As a result, the threads in the retaining strips and the mounting for the retaining strips become worn and eventually stripped. This leads to the necessity of replacing the strips and eventually the mounting for the strips as well. Double-sided tape is a better solution, in that installation, replacement and maintenance are all simpler, but the graffiti shield panel itself is more expensive than the simple panel which can be used with the retaining strips.
Also, there are installation difficulties inherent in a dual glaze bus window system. The largest single problem is moisture intrusion between the two glazing plies. If there is an insufficient gap between the two plies, the water and/or moisture that may get in between the plies due to washing or normal condensation processes, may not drain properly. If this should occur and the trapped water cannot drain out properly, salt encrustations can form in between the window plies, and unacceptable optical coupling occurs when moisture is present.
Another problem typical in a dual glaze bus window system is that the sacrificial window (graffiti shield) is made of a relatively soft material, such as acrylic. If that material comes into contact with the structural glazing, such contact can create clouding or scratching due to the abrading of the window guard by the glass.
A solution which would allow the easy installation and replacement of inexpensive graffiti shields and that allows for proper drainage of any trapped moisture that happens to accumulate between the graffiti shield and the window and that keeps the graffiti shield and window sufficiently apart to prevent a damaging interaction would be an improvement in the art and of great public value.
Another problem with existing bus window systems is that the vast majority of windows in buses, trains, and other vehicles are installed in frames that surround the window on all sides to a minimum depth of 1/2 inch. Due to this depth of installation, when the window glazing is damaged or vandalized, much or all of the frame structure must be removed from the vehicle or disassembled before the window can be replaced. This time consuming process often requires 2 to 4 hours.
Quick change windows are becoming available, but the cost of retrofitting an entire vehicle is often very high. A solution which would provide a less expensive method of retrofitting existing window frames to make them quick change windows would be an improvement in the art and of great public value.